Method of milling diatomaceous earth



. Feb. 19, 1935. McKlNL EY STOCKTON r 1,991,583-

METHOD OF MILLING DIATOMACEOUS EARTH Filed Nov. 27, 1931 Elf/700a l/mace.

A TTOANE Y Patented Feb. 19, 1935 g I 1 991 533 UNITED STATES PATENT OFFICE METHOD OF MILLING DIATOMACEOUS EARTH McKinley Stockton, Los Angeles, Calif., assignmto The Dicalite Company, Los Angeles', Calif., a corporation of Delaware Application November 27, 1931, Serial No. 577,498

2 Claims. (Cl. 83-94) This invention relates to a milling method and The invention is illustrated by wayof example particularly pertains to a method of reducing in the accompanying drawing inwhich the figdiatomaceous earth to a desired degree and charure is a diagrammatic view of a typical milling acter of fineness. plant, indicating the flow of the product there- 5 Diatomaceous earth in its native state occurs through.

in earth deposits from which it is mined, its Referring more particularly to the drawing, '10 natural form being consolidated and more or less indicates a crude-product bin into which lumps coherent masses of diatoms. These diatoms beof diatomaceous earth are deposited and from ing for the most part coarser than one micron in which they are carried by a conveyor 11 to a size. hammer mill 12 where they are reduced to the 10 In the preparation of an organic filter aid from form of small lumps. A conveyor 13 carries the these masses of diatomaceous earth it has been product to a storage bin 14. It is to be understood heretofore customary to reduce them to a desired that when the product is mined it carries a large degree of fineness by passing the diatomaceous percentage of moisture, and in fact, when it 15 earth through millingmachinerywhichfunctioned reaches the storage bin its moisture content both to disintegrate the masses while violently ranges from 35 to 60 per cent. The product is milling them and to convey the material through then withdrawn from the storage bill by a conthe apparatus. In such apparatus it has been cusveyor 15 and passes through a conduit 16 .(which tomary to employ milling machinery which inis in communication with a suitable auxiliary 20 eluded a swing hammer or beater arms operating furnace or with the kilns inwhich the product 20 in separate units, or such means in combination is subseque t y calcined) t0 a through a fan with high speed paddle wheel fans. These-fans 1'7 and thence to a cyclone separator 18 together have for the most part operated at a speed of with the heated air from the furnace. the order of 1700 R. P. M. with the tips of the During the conveyingoperation the earth prod- 5 paddle wheels traveling at a speed of approxinot with the heated air from the furnace must 25. mately 15,000 feet per minute while creating air pass through the fan 17 and may subsequently velocities of the order of 6000 feet per minute pass through other fans hereinafter to be deand moving air containing approximately one scribed. These fans are preferably formed'witha pound of diatomaceous earth to- 67 cubic feet of plurality of blades, the fans being approximately 0 air. After this milling the product has been 36inches in diameter and the blades being approx- 30 suitably conveyed, dried and milled, and sepaimately 18 inches in width. These dimensions of rated to predetermined degrees of fineness. In course, depend upon the amount of air which it is the use of such products it has been found that desirable to move in order to obtain the most efflthe milling method above described has for the cient results. I

most part destroyed or so damaged the structure In actual Operation it has been found that by 35 of the constituent diatoms that when used as a reducing th milling action 0f t e fan a ovfilter aid, the filtration rate of the milled product ing a larger Volume of air D unit of d is seriously reduced without any compensating ceous earth, as for example approximately'IS cubic improvement in the clarification of the filtrate. feet of air per pound of earth, a more desirable 40 It is the principal object of the present inproduct is obtained. The effect is to comminute 40 vention, therefore, to provide a method of milling the earth in a more gentle manner by the mutual diatomaceous earth whereby the earth may be collision of the particles while suspended in the reduced to a desired degree of fineness with the rapidly moving air, rather than by collision with preservation of a maximum percentage of the the fan blades and the case, and they e thus diatoms in their original structural form, thereby reduced to a desired degree of fineness without 5 obtaining a product having a relatively rapid materially damagingthe original structuralform I filtration rate and a high clarifying power. of the constituent diatoms.

The present invention contemplates the use of In carrying out the present invention I find apparatus heretofore employed in practicing any that when the paddle wheel velocities are held method of milling diatomaceous earth and kinwell below a. tip speed of 15,000 feet per minute; as 50 dred products, but in which this apparatus is for example, tip speeds ranging from9600 feet used in such manner as to obtain a product havper minute up to 14,000 feet per minute, the ing greater clarifying efficiency than is commonly diatoms are not seriously broken, and at this rate obtained, and by a novel method which will be of speed it has been easily possible to double the hereinafter set forth. flow rate of diatomaceous earth filter aid with- This isa surprising 'phenomenomjsincg it has always been assumed in the art that the character of the fine particles produced in similar systems of milling were characteristic of. the earth itself and not the manner in which it is milled.

terially improved by operating the fans at lower speeds and without the harsh milling formerly practiced.

It has also been found desirable to drive the. fans 17 by a variable speed motor 19 so that the optimumfan speed may be established for any quality or condition of. raw earth to be treated After the comminuted prod-L in-the apparatus. not. in a partially dried state has been passed through the cyclone separator 18 its moisture content will be of the order of 25 to 30 per cent. It is then carried through a conduit 20 and delivered to a conduit 21 where it is further dehy- 'drated by hot gases from a furnace 31 in passing through by the fan 1'7, which is of similar construction to the one previously described. A conduit 22 leads the product to a collector and classifier 23, from which a'desired product is caused to pass through a conduit 24 to anothercyclone separator 18', at which point ,the prodnet is of a state of dehydrationin per cent. 1

It is understood that this cycle of operation might be repeated any desired number of times; for example, with the product in a desired degree of fineness and of dehydration, it may then be fed through conduit 25 by a fan 1'7" and then through a conduit 26 to a third cyclone separator 18", or if desired, it may be fed to a conveyor 27 by which it will be conducted into a kiln 28. Within this kiln it is subjected to the action of heat tending to remove the associated organic matter and to cause the particles to acquire a more porous character which willren der them highly desirable filter .aids.

The calcined product will then flow from theend of the kiln 28 to a cooler 29 and may thereafter be suitably conveyed and stored.

Attention is particularly directed to the methd of drying here practiced, since it has been found that where materials heavily laden with moisture are introduced into the plant and rapidly dried severe milling effects are produced. This is due to the fact thatthe wet earth seems i to be more sensitive to milling 'conditions and under any ,v'iolent impact qr abrasion breaks down-toe much finer degree than'where the product has been gradually temp'ered'with heat and gradually dries without destroying its or--v iginal structure. The previous rapid drying methods have materially reduced the utility of the product as a filter aid as comparedwith a product which is pre-dried and fed through the milling system while containing less than 25 perv n w 1',991,58 3 out in any way" impairing its clarifying: power;

the order of 'heated gas, through earth to a drying operation and moving water to cent moisture. The latter product has proven to be less friable and the particles are of a more uniform size, the wasteful destruction of usable material by the breaking down of the diatom structure being avoided.

A suitable. pre-dryer is indicated at 35 in the drawing-and is. interposed between the bin 14 and the pipe -16. This predryer may be of any desired'type, as'a hearth, mufile or rotary kiln, but in whatever form it must be of such dimensions as to retard-theflowof earth and remove the desired proportion of water from the lump earth at such relatively low temperature as will not glaze or sinter thelumps. r

Attention is further directed to the fact that the customary speed of a swinghammer or beater arm mill is approximately 1200 R. P. M., and

it has been found that by'reducing the range of speed of this mill to from 500 to 1000 R. P. M.,

the resulting product will contain less broken diatoms, giving a superior flow rate as a filter aid with equal clarifying power.

It will thus be seen that the method here disclosed contemplates the handling and. comminution of diatomaceous earth with as small amount of violent motion and attrition as possible, while reducing the product to a predetermined degree of fineness and dryness without'materially breaking down the structure of the diatoms.

While I have shown the preferred form of my method as now known to me it will be understood that various changes might be made in the steps of the operation and the order of the steps without departing from the spirit of the invention as claimed.

Having thus described my invention, what I claimand desire to secure by" Letters Patent 1. A method of comminuting diatomaccous earth which comprises: reaking the crude moist earth to smaller lumps; subjecting said lumps to a slow predrying operation and reducing the water content of said lumps to approxi-' mately 25% by weight, and thereafter passing said predried lumps, together with a stream of a comminuting operation in which drying and communition are simultaneously completed.

2. The method of producing a dried and comminuted diatomaceous earth product which includes thefollowing steps in the order stated: partially comminuting the crude moist earth by passing said earth through a swing-hammer mill; subjecting the partially comminuted moist partially recnly such extent as to render the earth particles'readily friable, and finally suspending said partially comminuted and partially dried earth in a stream of heated gas and completing the drying and comminution of said earth while in said suspension.

McKINLEY STOCKTON. 

